South African city lights beneath a curved glowing atmospheric horizon and stars, viewed from the ISS.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Earth rotates eastward. 15° per mean solar hour. Sun direction held fixed.

9.60 hours of rotation · 144.0°. West-to-east rotation brings successive places into sunlight. Day and night come from geometry, not time-zone boundaries.

Earth rotation and the terminator

Explain how Earth’s eastward rotation produces day and night, and relate a 15° difference in longitude to one hour of solar time.

Drag to rotate. Hold Ctrl and scroll to zoom, or pinch on a touch screen.

Why it happens

Earth turns eastward, carrying each location into sunlight and then darkness. The boundary between day and night is called the terminator; it separates the illuminated and unilluminated halves of Earth.

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South Africa on Earth's night side, seen from the ISS. Rotation carries locations through sunlight and darkness; this is a photograph of the night hemisphere.

Try a comparison

Pause and move the Day slider. Compare a quarter-turn with six hours of a mean solar day, then explain why the bands do not determine Earth’s rotation.

Reading the result

The time-zone bands divide longitude into ideal 15° intervals; actual civil time zones follow local decisions and borders.

A common misunderstanding

Time zones determine where day and night occur.

Earth’s rotation carries places into and out of sunlight. Time zones assign civil clock times to regions; their boundaries reflect political and practical choices. Changing a time-zone boundary would change the clock label, while sunrise and sunset would still follow Earth’s rotation and the Sun’s direction.

Cases

Day0.40